How long can someone survive without water?

Not as long as aspiring Buddhas may claim. Reports from Nepal tell of a teenage boy who has been meditating for the last six months and is said to have not drunk any water for the entire period. Crowds are flocking to worship Ram Bahadur Bamjan, who is sitting cross-legged under a tree in the village of Ratanapuri. To gain enlightenment, like Buddha did more than two and a half thousand years ago, he needs to continue the process for another six years. Now suspicious locals have asked for a scientific examination to determine if the boy is managing without water.

The magician David Blaine survived 44 days without food, losing one quarter of his body weight, but keeping a healthy body mass index. In 1976 obese people were put on an experimental starvation diet, with absolutely no food, for 40 days and none of them had any trouble surviving. "It is possible to last much longer without eating than without drinking," says Martha Stipanuk, from the division of nutritional sciences at Cornell University in New York. But it does depend on your initial body condition. "A weak elderly person, or thin young person might not be able to go very long without food," she adds.

The problem for wannabe Buddhas is that surviving for weeks without water is not an option. "People can last a few days without water depending on the environment in which they find themselves and whether [they are] injured or not," says Jeremy Powell-Tuck, professor of clinical nutrition at Barts and the London Queen Mary school of medicine, who supervised Blaine's recovery.

Someone sitting quietly under a shady tree will be better off than an explorer caught out in the middle of a blazing desert, but nonetheless they won't be able to survive six months without a sip of water.

"Without water anyone will run into problems pretty quickly. Their blood volume will shrink and their water and electrolyte balance will be upset. Eventually the body will just go into shock," says Professor Stipanuk.